Method of producing a white, platinumlike color chromium plate and the product thereof and bath therefor



Pam-a Jan. 5, 1943 2,301,551 Ma'mon or raonucmo, a warm, rm'r- THEREFORCOLOR CHBOMIUM PLATE AND THE PRODUCT THEREOF ANDBATH Joseph John Trisha,Ea'st Elmhurst, N. Y., as-

signor, by direct and meme assignments, to

te Corporation, I eration of New York New York, N. Y., a cor- NoDrawing.Application August 19, 1939,

Serial No. 291,040

The present invention relates to an improved process for chromiumplating articles of manufacture with an ornamental and/or protectiveplate having a white, platinum-like color and being substantially devoidof a bluish tint or purplishcast, to a product of such a process, and

" to a bath therefor.

It is well-known that thechromium plate produced by conventionalelectroplating processes possessed a highly objectionable bluish tint orpurplish cast. In some industries, the bluish tint or purplish cast hasbeen so objectionable as to reduce the value of the chromium plate or torender it unacceptable or unsalable. This has been particularly true inthe Jewelry trade where white and platinum-like color has been'desiredand has commanded a premium, while the bluish or purplish casts or tintsof conventional chromium plating having been objected to by jewelers,merchants and the public. Even in the sanitary industry or plumbingtrade, a demand has arisen for'a white chromium plate whereas theconventional bluish chromium plate has fallen into disfavor. Similarly,other industries wanting a "live plate have desired a white chromiumplate instead of the "dead" plate of the customary bluish chromiumplate. The shortcomings and disadvantages of the bluish chromium plateof prior art processes of chromium electro-plating including the Finkprocess (U. S. Patent No.

1,496,845), the Hambuechen process (U. S. Patent No. 1,544,451)and-other processes have been known to those skilled in the art.Although the investigators have been diligently endeavoring to solve theproblem confronting the art, no wholly satisfactory and successfulprocess has been proposed to produce an acceptable plate having a whiteand platinum-like tially devoid of a bluish I have discovered animproved process of electro-plating chromium which avoids the occurrenceof a bluish or purplish plate and which pro duces an attractive whiteand platinum-like colored plate.

It is an object of the color which is substanor purplish cast.

present invention to provide an improved process of chromium plating onarticles of manufacture with a white, platinum-like color. 7 It isanother object of the present invention to provide a bath platinum-likecolored chromium plating.

It is a further object to provide articles of manufacture plated withchromium having a white, platinum-like color devoid of a bluish orpurplish tint.

.for electro-dcpositing white,

5 Claims. (Cl. 204-51) Other objects and advantages of the inventionwill become apparent from the following description.

Broadly stated. my invention comprises adding to any appropriatecommercial or practical chromium plating solution metallic cadmium or anoxide of cadmium or a salt of cadmium, and then subsequentlyelectrolyzing the plating solution to electrodeposit a white,platinum-like chrome plate.

It is to be observed that my new whitish, platinum-colored chromiumplate is more resistant to rusting than the conventional chromium plate.This was shown by the results obtained by plating nails in theconventional chromium plating solution and plating similar nails in myimproved chromium solution by my improved process and subsequentlysimultaneously exposing both groups of nails to the weather. Those nailsplated with conventional chromium showed signs of rust before the end ofa four month period while the others showed no signs of rusting.

For the purpose of giving those skilled in the art a betterunderstanding of the following illustrative examples. are given.

Example No. 1

A chromium plating bath is made bydissolving about 300 grams chromicacid per liter or about 10 ounces of chromic acid in a quart of water,and adding about 3 cubic centimeters of concentrated sulfuric acid. Whenall of the diromic oxide is in solution about 10 to about 40 grams ofcadmium metal or preferably about 15-20 to about grams of cadmium oxideor the equivalent amount of cadmium salt per quart are added. Thesolution is kept at the proper temperature (80 to 110 F.) andelectrolyzed for a suitable period of time, depending upon currentdensity and volume of the bath, preferably about three to about fivehours for a 10,000 gallon bath, at a potential diil'erence of about fivevolts or until the cathode has been coated with a thin deposit. In orderto determine whether or not the bath is in a condition permitting thedeposit of a white,

The temperature is maintained at about F.

invention, the

to about 110 F. A chromium plate is obtained which has a white,platinum-like color practically devoid of bluish and purplish hues. The

throwing power of the present improved plating solution is increasedover that of the conventional chromium plating solution. In someinstances, an increase of throwing power up to Throwing Power ofChromium Plating Baths With the Cavity Scale Test Metal Cleaning andFinishing, October 1930, page 851.

Example No. 2

Into an electrolytic cell containing sumcient water and sufiicientchromium tri-oxide, an appropriate amount of sulfuric acid and ofchromium hydroxideare introduced to bring the concentrations to about250 grams of CrOs, about 3 grams of H2804 and about 6 grams Cr(OH)'a perliter; .When solution is complete, about 10 to about 40 grams of cadmiumor about 12 to about 45 grams cadmium oxide or the equivalent of cadmiumas. a salt are added per liter. The bath is "pretreated for a period oftime, say for about one hour for a bath having a volume of 100 gallons,at the normal working temperature of the bath (about 80 to about 110 F.)at a potential difference of about 5 volts and a current density ofabout 0.75 amp. sq. in. or until a test strip immersed in the bath hasdeposited thereon a white, platinum-like deposit. The articles to beplated are then connected as a cathode and a coating of white,platinum-colored chromium is deposited at a current density of about 40to about 110 amperes per square foot at a voltage of about 4 to about 6volts. The temperature is maintained at about 80 F. toabout 110 F. or atthe. working temperature of the bath. A chromium plate is obtained whichhas a white, platinum-like color substantially without any blue orpurple hue.

Example N0. 3

For the purpose of depositing the new platinum-colored plate. ofchromium by electrolysis of a solution containing chromium and cadmium,a fluoride bath similar to the fluoride bath of Hambuechen, etc. ismade. About 800 grams of chromic acid and about grams of sodium fluorideor about 8 grams of hydrofluoric acid are addedto one liter of water orproportional quantities to larger volumes of water. When the solution ofthese ingredients has occurred about 10 to about 40 grams of cadmium orabout 12 to about 45 grams of oxide of cadmium per quart or anequivalent amount of a soluble salt of cadmium are added. The solutionis warmed until the temperature is about 36 to about 45 C. The bath ispretreated" as described heretofore. The articles to be plated are madethe cathode in an electric circuit and plated with a white,platinum-like coating substantially devoid of a bluish or purplish castor tint by passing a current through said electric circuit at apotential difamount of material plated, the deposit on the articles willhave a tendency to become bluish or purplish. As soon as the bluish orpurplish cast appears, the normal plating operation is discontinued. Thecolor of the plating may be restored by replenishing the supply ofcadmium in the bath. This may be done conveniently by placing, one ormore sticks of cadmium metal in the bath or by the addition ofsuificient cadmium oxide to restore the metal concentration to theoriginal one. In order to determine whether or not the bath is in acondition permitting the deposit of a white, platinum-like colorchromium plate test strips are immersed from time to time during the"pretreatmen period. The bath is ready for use when a test strip iscoated with a deposit of white, platinum-like color. I have found thatin general the increase of the cadmium content of .the bath to aconcentration above 45 grams of cadmium or its equivalent of cadmiumcompounds produces a gray deposit which is burned on the'edges.Simultaneously, the throwing power of the bath is reduced. Theconcentration of cadmium should preferably be controlled within criticallimits for best results.

I have also found that the cadmium may be alloyed with the'anodematerial, for. example,

ference of from about 3 to about 6 volts at a longer or shorter periodsdepending upon the with the leadof the anode and in thatway cadmium maybe introduced into the bath.

In producing my new whitish, platinum-colored chromium plating I haveobtained satisfactory results with electrolytes containing cadmium andchromium as the major metallic constituents and containing as minorconstituents mainly lead and antimony together with lesser amounts ofzinc, tin, copper, manganese, magnesium, iron, aluminum, thallium. Leadand antimony present to the extent of a fraction of a percent to about1% give satisfactory results. In practice I have employed cadmium oxidewith a lead content of about 0.5% and an antimony content of about thesame order of magnitude and obtained very satisfactory results.

Platings produced in a bath having the compositions indicated above havebeen found to contain small amounts of lead such as about 0.0001 toabout 0.003%. Whether thenew results are dependentupon the presence oflead in the plating or whether the modifying elements combine to afiectthe development of the crystals of the chromium plating has not beenestablished nor has the verity of any other theoretical explanation beenestablished. Nevertheless, my.-

new whitish, platinum-colored chromium plate is readily recognizedwhether in bright finish or matte finish or in other finishes by thepractically total absence of reflection in the bluish or purplish rangeof light.

I have found that in order to obtain a whitish, platinum-coloredchromium plate it is necessary to pro-treat or electrolyze aconventional chromium plating bath adapted to produce a chromium platehaving bluish or purplish hues after modification by the addition ofadditional elements as described hereinbefore. The pretreatment may becarried out at various current densities and for periods of timecorrelated with the electrode area, the volume of the bath and thecurrent density. Thus, for small baths having a volume of a liter or so,the "pretreatment may be carried out at a current density of about 0.5amp/sq. in. At such a current density a pretreatment for a period of afraction of an hour, say 20 minutes is suflicient. A commercial bath of,say, gallons capacity may likewise be converted from one producing abluish chromium plate to a bath capable of producing my new whitish,platinum-colored chromium plate by pretreating after the addition ofmodifying elements at a current density of about 0.75 amp/sq. in forexample, for a fraction of an hour, say, one half hour, to about anhour. Similarly, a 500 gallon bath after pretreatment for about 1.5hours to about 2 hours at a current density of about 0.75 amp/sq. in.likewise may be employed for the production of my improved chromiumplating substantially devoid of bluish and purplish hues. Asillustrative which the pretreatment of a 1,000 gallon bath, modified asdescribed hereinbefore, may be carried out is as follows: the currentdensity employed may be about 0.75 amp/sq. in. and the bathelectrolyzedfor about 2.5 to about 3 hours. I have also obtainedsatisfactory results by pretreating a conventional chromium bath of10,000 gallons capacity and modified in accordance with the principlesof the present invention for a period of about 3 hours to about 5 hoursat a current density of about 2.5 amperes per square inch. From theforegoing it will be appreciated by those skilled in the art thatvarious changes may be made in the conditions of pretreatment withoutdeparting from the spirit of the present invention provided thepre-treatment of a conventional chromium plating bath only capable ofproducing a bluish or purplish chromium plate results in the productionof my whitish, platinum colored chromium plat ng. The extent andefficiency of any set of conditions of pre-treatment is clearlydetermined by means of a test strip.

When the deposit on a test strip plated in a conventional chromium bathmodified in accordance with the principle of the present inventionbecomes a whitish, platinum-color the pre-treatment may be discontinuedand commercial use of the bath proceed.

Certain modification in the procedure permit plating various finishes onvarious bases. For example, a matte finish may be obtained byinterrupting the current during the plating 01 an article. A hard finishmay be obtained by controlling the amount of sulfates in the bath. Forexample, it has been found that with about 250 grams of chromic oxideper liter that about 3-4 grams of H2804 per liter give hard deposits ata voltage of about 3.5 to 4 volts. On the other hand, a soft ductilepate may be obtained by operating at hi her than normal workingtemperatures, say at about 115 F., with normal current densities.

Iron or steel may be plated directly after conventional cleaning inacustomary manner or after applying a preliminary nickel or copperplate. Nickel or German silver can be plated directly after conventionalcleaning, while brass, copper and bronze may be plated directly or aftera previous nickel plate. Tin or silver is plated with my new white,platinum-like plate after preliminary plating with nickel. Silver whenplated directly has a "matte finish. Zinc, a uminum and lead diecastings can be plated with my new whitish, platinum-colored chromiumcoating after being made practically chemically clean and plated withcopper, the usual current densities and temperatures.

The thickness of the deposit by the time taken for plating. For example,a good commercial deposit for the Jewelry trade may be obtained in aboutto minutes under normal conditions. For plating dies, tools, etc.,

of the conditions under.

duced consistently Type of finish Time for .Time for heavy light plateScientific explanations sults obtained by at the present time. my white,platinum-like alloy finish can be proof the remarkable rethispretreatment are unknown It sufiices, however, that upon a practicalscale by the use of my pretreatment in conjunction with my novelelectrolyte and process.

It is .to be observed that further modifications of my process canbemade. For example, boric acid, tartaric acid, citric acid, oxalicacid, and mono-sodiuni, di-sodium and trisodium phosphates may be addedto commercial chromium plating solutions as. modifiers.- The addition ofthese modifying agents in amounts up to about 20 to about 30 grams perliter makes possible the addition of increasing amounts of cadmium oxideor other sources of cadmium. In the presence of from about 10-20 gramsof boric acid per liter, for example, the quantity of cadmium oxide maybe increased to about to about grams per liter without the depositlosing its white, platinum-like finish or showing signs of burning.Likewise with 10 to about 30 grams of oxalic acid and the othermodifiers enumerated hereinabove the quantity of cadmium oxide which maybe added without deleterious effect upon the finish may be increased toabout 160 grams per liter. The phosphates noted herein above may be usedseparately or in combination with tri-sodium phosphate.

It was surprisingto find that the addition of hydrofluoric acid metalfluoride (NaF, KF, etc.) as a modifying agent to the conventional Finksulfate bath permits the cadmium oxide content to be raised to about 160grams per liter without deleterious effects.

It is to be observed that the present invention provides a chromiumdeposit which to the unaided eye does not reflect light of the wavelength of blue or purple range of the spectrum.

shows the practically total absence of reflection in the blue or purplerange. This may be assumed to be a result of grain size although I donot wish to be limited to this explanation. For, whatever may be theexplanation of the cause of the absence of bluish and purplish hues frommy new whitish, platinum-colored chromium plate, the fact neverthelessremains that any conventional, commercial, industrially practicalchromium bath which is modified and pre treated in accordance with theprinciples of the present invention produces my new whitish,platinum-colored chromium plate.

Although the present invention has been described be understood thatvariations and modifications may be resorted to as those skilled in theart will readily understand. Thus, when a chromium skilled in the art.Furthermore various articles of manufacture may be plated includingbracelets, chains, rings, vanity cases, lipstick cases, optical frames,cigarette cases, cigar lighters,

watch cases, hollow and tableware, jewelry and novelty work, surgicalinstruments, plumbing ware, ornamental iron and bronze fittings forshow-windows, display fixtures, hardware, lighting fixtures, kitchenutensils, ofiice articles, inkstands, letter openers, automobile partsand accessories, reflectors, etc., etc.

the purview of the-present specification and the scope of the appendedclaims.

The present application is a continuation in partof :myco-pendingapplication, Serial No.

119.628; filed in the U. S. Patent Oflice on Janj :1. A method forprovidingarticles with a chromium electroplating having a white,platinumlike color substantially devoid of bluish and purplish' hueswhich comprises preparing a chromium plating bath for the industrialelectrodeposition of a conventional electroplate of bluish chromium,said bath containing chromic acid and a chromium plating catalystcomprising an acid radical and having immersed therein an electrodesurface, adding at least about 13 to about 1'! grams to about 35 gramsof metallic cadmium and up to about 1% of lead and antimony per liter tosaid bath, pretreating said bath by passing a current between an anodeand a test cathode immersed therein at a current density of about 0.5 toabout 2.5 amperes per square inch and at about 5 volts for a'period oftime varying from a fraction of an hour to several hours until a testplate shows awhite, platinum-colored deposit of chromium substantiallydevoid of bluish and purplish hues, making an article to be plated withplatinum-colored chromium the oathode of said. electrolyzed bath,passing an electric current through said electrolyzed chromium bath at apotential difference of about 3 to about 6 volts at a current density ofabout 40 to about 110 amperes per square foot while maintaining the bathat a temperature of about 80 to about 110 F., continuing to plate asuccession of artides in said electrolyzed bath until an article being.plated begins to show bluish and pur-' plish hues, adding suiiicientmetallic cadmium to said bath to bring the concentration of cadmium toat least about 15 to about grams to about 30 .grams of cadmium perliter, then continuing to plate the said bath and repeating the Suchvariation and modifications are considered to be within void of bluishand purplish hues, making an aring catalyst comprising an acid radicalfor industrial plating of conventional bluish chromium electroplating,including in said bath at least 13 grams per liter of cadmium, aneffective amount up to about 1% of lead and antimony and an amount ofmodifier-up to about 30 grams per liter selected from the groupconsisting of boric acid, hydrofluoric acid, alkali metal fluorides andmono-, diand tri-sodium phosphates, whereby the amount of cadmium whichmay be included inthe aforesaid bath may be greater than 35 grams ofmetallic cadmium, said bath having an electrode surface immersedtherein, pretreating said bath by passing a current between an anode anda test cathode immersed therein at a current density of about 0.5 toabout 2.5 amperes per square inch and at about 5 volts for a period oftime varying from a fraction of an hour to several hours until a testplate shows a white, platinum colored deposit of chromium substantiallydeticle to be electroplated with chromium the oathode of saidelectrolyzed bath, and passing an electric current through saidelectrolyzed bath at a potential difference of about 4 to about 6 voltsat a current density of about 40 to about 110 amperes per square footWhile maintaining the temperature of said bath at about to about F.,whereby an article is electroplated with a white, platinum-like chromiumelectroplating containing cadium and substantially devoid of bluish andpurplish hues.

3. An electroplating bath for use in electrodepositing white,platinum-like chromium electroplatings substantially devoid of bluishand purplish hues constituted principally of chromium comprising asolution containing chromic acid and a chromium plating catalystcomprising an acid radical in amount suflicient to produce commercialbluish chromium electroplatings, at least 13 grams per liter of cadmium,an eiiective amount of lead and antimony up to about 1% and an amount ofmodifier up to about 30 grams per liter adapted to make possible theaddition of increased amounts of cadmium up to about grams per liter andbeing selected from the group consisting of boric and hydrofluoric acid,

alkali metal fluorides and mono-, di-, and trisodium phosphates, saidbath having been pretreated by passing a current between an anode and atest cathode immersed therein at a current density of about 0.5 toabout.2.5 amperes per square inch and at a. potential difference ofabout 5 volts for a period of time varying from a fraction of an hour toseveral hours until a test plate shows a white, platinum colored depositof chromium substantially devoid of bluish and purplish hues andcapable, only after such pretreatment, of electrodepositing white,platinum-like chromium platings substantially devoid of bluish andpurplish hues.

4. An electroplating bath for use in electrodepositing chromiumelectroplatings constituted principally of chromium and cadmium inamount effective to produce a white, platinum-like deposit comprising asolution containing chromic acid, a chromium plating catalyst comprisingthe fluoride radical sufficient to deposit conventional bluish chromiumelectroplating commercially, an effective amount up to about 1% of leadand antimony and an amount of modifier up to about 30 grams per literadapted to make possible the addition of increasing amounts of cadmiumand at least 13 grams to about 160 grams of cadmium per liter, said bathhaving been pretreated by passing a current between an anode and a miumplatings substantially devoid oi bluish and test cathode immersedtherein at a current denpurplish hues.

sity of about 0.5 to about 2.5 amperes per square 5. As a new article ofmanufacture, an elecinch at a potential diflerence of about 5 volts fortroplated article having a white, platinum-cola period of time varyingfrom a fraction 01' an 5 ored plating of electrodeposited chromiumconhour to several hours until the test plate shows taining about 0.0001to about 0.003% lead, said a white, platinum colored electrodeposit ofchroplating being substantially devoid of bluish and mium substantiallydevoid of bluish and purplish purplish hues.

hues and capable, only after such pretreatment, JOSEPH JOHN TRISKA. oielectrodepositing white, platinum-like chroi0

